JPH075664B2 - Method for reducing sheeting in polymerizing α-olefins - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for reducing sheeting in polymerizing an α-olefin, and more particularly to a method for reducing sheeting in polymerizing ethylene. .

Prior Art As is well known to those skilled in the art, low pressure high density or low density polyethylene is prepared by the fluidized bed process using several catalysts to produce a wide range of low density and high density products. Can be conveniently supplied now. The appropriate choice of catalyst to be utilized depends in part on the type of end product desired (ie high density, high density, extrusion grade, thin film grade resin) and other criteria, and is generally for example July 30, 1985. It is described in US Pat. No. 4,532,311 issued on the date.

Generally, the catalyst is introduced with the polymerisable feedstock into a reactor with an enlarged section above the straight side section. The recycle gas enters the bottom of the reactor and passes through the gas distribution plate upward into a fluidized bed located in a section on the straight side of the vessel. The gas distribution plate ensures proper gas distribution and acts to support the resin bed when the gas flow is stopped.

The gas flowing out of the fluidized bed carries the resin particles. Most of these particles leave as the gas passes through the widening section and slows down.

Unfortunately, the use of certain catalysts shown as type IV catalysts in the above U.S. patents as well as vanadium-based catalysts is used as sheeting during the production of polyolefins by polymerizing alpha-olefins in a fluidized bed process. Have a tendency to cause

These types of catalysts (ie, type IV catalysts) have been used to satisfy certain end uses for ethylene resins, such as thin film, injection molding and rotomolding applications. However, attempts to produce some ethylene resins using type IV catalysts or vanadium-based catalysts supported on porous silica supports in some fluidized bed reactors have been entirely from a practical point of view. Is not satisfied. This is mainly a "sheet" in the reactor after a short period of operation.
Is formed. This "sheet" can be characterized as comprising the fused polymeric material.

These sheets vary widely in size, but are similar in most respects. These are generally about 1/4 to 1 thick
1/2 inch, about 1 to 5 feet in length, some samples are much longer. These are about 3 inches
Has a width of 18 inches or more. These sheets have a core composed of a fused polymer oriented in the longitudinal direction of the sheet, the surface of which is covered with a granular resin fused to the core. The edges of the sheet may have a hair-like appearance due to the strands of fused polymer.

After a relatively short period of time during the polymerization, sheets begin to emerge in the reactor and these sheets block the product discharge system leading to shutdown of the reactor.

Therefore, it will be seen that there is a current need to improve the polymerization techniques required to produce polyolefin products using titanium-based catalysts in fluidized bed reactors.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a method for substantially reducing or eliminating the degree of sheeting that occurs during low pressure fluidized bed polymerization of an α-olefin using a titanium compound as a catalyst. To provide.

These and other objects will become more apparent from the following description with reference to the accompanying drawings.

[Means for Solving the Problems] In a broad sense, the present invention is arranged in a circulation path for circulating a circulation flow composed of unreacted gas and solid particles, and in the circulation path for cooling and compressing the circulation flow. In a gas-phase fluidized reactor equipped with a cooling means and a compressor means, using a titanium-based catalyst or other catalyst having a tendency to cause sheeting when a sheet-forming amount of water or oxygen is present as impurities, α -When polymerizing an olefin, a gas feed stream consisting of a monomer, a comonomer, an inert gas and hydrogen, the gas feed stream comprising a sheet-forming amount of oxygen or water as impurities of the gas feed stream;
Introducing the recycle stream into the cooling means prior to cooling, then cooling the recycle stream and the gas feed stream and directing them to the reactor for sheeting during polymerization of the α-olefin. Provide a reduction method.

It has been found that the amount of static voltage generated by the addition of impurities such as oxygen or water to the fluidized bed polymerization reactor is highly dependent on the point of addition of impurities to the cycle. The sites of doping that cause the greatest electrostatic response are directly in the stagnant region of the fluid in the fluidized bed. When impurities are injected into the cycle far away from the fluidized bed (eg upstream of the circulating gas cooler), the static charging effect that occurs is significantly diminished. Therefore, according to the present invention, a feed stream of monomers, co-monomers, nitrogen and hydrogen to the process (these feed streams optionally containing electrostatically generated impurities such as water or oxygen) is provided upstream of the circulating gas cooler. Positioning reduces static charging. The reduction of static charge in the fluidized bed leads to better reactor performance by reducing the risk of sheet and chunk formation, which is often a direct result of static electricity. The invention minimizes sheeting, and thus eliminates the downtime that occurs to remove these sheets.

With particular reference to the accompanying drawings, a conventional fluid bed reaction system for polymerizing α-olefins comprises a reactor 10 consisting of a reaction zone 12 and a rate reduction zone 14.

The reaction zone 12 comprises a bed of increasing polymer particles, formed polymer particles and small amounts of catalyst particles, which bed is a continuous stream of polymerizable and modifying gas components as make-up gas and recycle gas flowing through the reaction zone. It is fluidized by the flow. To maintain the pot fluidized bed, the mass gas flow to the bed is generally maintained higher than the minimum flow required for fluidization, preferably from about 1.5 times to about 10 times G _mf, and more preferably of G _mf About 3
Is about 6 times. G _mf is used as accepted as a symbol for the minimum gas flow rate required to achieve fluidization [CY Wen and YH Yu, "Mechanics of Fluidization", Chemical Engineering Process Symposium Series 62, 100-111 (1966)].

It is highly desirable that the bed always contains particles to prevent the formation of localized "hot spots" and to entrain and distribute the particulate catalyst throughout the reaction zone. When starting,
The reactor is generally charged with a base of particulate polymer particles before the gas flow is started. These particles may be identical in nature to the polymer to be produced or they may be different. If different, they are withdrawn as the desired product polymer particles as the first product. Finally, a fluidized bed of the desired polymer particles replaces the starting bed.

Suitable catalysts used in the fluidized bed are preferably stored under a gas seal in storage tank 16 until use, the seal gas being a gas inert to the storage material such as nitrogen or argon.

Fluidization is accomplished by high flow gas circulation to the bed, which is typically about 50 times the feed rate of make-up gas. A fluidized bed has the general appearance of a dense mass of workable particles in a free vortex that can be formed by gas permeation into the bed. The pressure drop across the bed is equal to or slightly greater than the bed mass divided by the cross-sectional area. Therefore, this depends on the geometry of the reactor.

Make-up gas is fed to the bed at a rate equal to the rate at which the particulate polymer product is withdrawn. Make-up gas composition is determined by a gas analyzer 18 located above the bed. The gas analyzer measures the composition of the gas being circulated and the composition of the make-up gas is adjusted accordingly to maintain a near steady state gas composition in the reaction zone.

To ensure complete fluidization, recycle gas and, if desired, part or all of the make-up gas at the base below the floor.
Return to the reactor at 20. The gas distribution plate 22 located above the return point ensures proper gas distribution and supports the resin bed when the gas flow is stopped.

The part of the gas stream that does not react in the bed constitutes the circulating gas, which is preferably removed from the collecting zone by transferring it into the velocity reduction zone 14 above the bed, where entrained particles are You will be given the opportunity to fall back into the floor.

Then heat exchanger after being compressed by circulation compressor 24
After passing through 26, where heat of reaction is removed, it is returned to the floor. Due to the constant removal of the heat of reaction, there seems to be no appreciable temperature gradient above the bed. The temperature gradient exists as a bed of about 6-12 inches at the bottom of the bed and results in a temperature between the temperature of the incoming gas and the temperature of the rest of the bed. Thus, the bed acts above the bottom layer of this bed zone to adjust the temperature of the circulating gas almost immediately to match the temperature in the rest of the bed, thereby acting to maintain a near constant temperature under steady state conditions. Was observed. The recycle stream is then returned to the reactor at its base 20 and via distribution plate 22 to the fluidized bed. The compressor 24 can also be installed downstream of the heat exchanger 26.

Hydrogen can be used as a chain extender in conventional polymerization reactions of the type contemplated by this invention. When ethylene is used as the monomer, the hydrogen / ethylene ratio used will vary from about 0 to about 2.0 moles of hydrogen per mole of monomer in the gas stream.

According to the invention, a feed stream (gas stream) of hydrogen, nitrogen monomers and comonomers is introduced into the gas circulation stream before the point where the circulation gas stream flows into the heat exchanger 26, for example via the path 42. To do.

Any gas that is inert to the catalyst and reactants can be present in the gas stream. The co-catalyst is added to the gas recycle stream upstream of the connection to the reactor from dispenser 28 via line 30. As is well known, it is essential that the fluidized bed reactor be operated below the sintering temperature of the polymer particles. That is, to ensure that sintering does not occur,
Operating temperatures below the sintering temperature are desirable. To produce ethylene polymers, preferably operating temperatures of about 90-100 ° C are used to produce products having densities of about 0.94-0.97, whereas for products having densities of about 0.91-0.94. Temperatures of about 75-95 ° C are preferred.

Generally, fluidized bed reactors are operated at pressures up to about 1000 psi, preferably at pressures of about 150 to 350 psi, with higher pressures in this range being suitable for heat transfer.
This is because increasing the pressure increases the unit volume heat capacity of the gas.

The catalyst is injected into the bed at a rate equal to its consumption at point 32 above distributor plate 22. The catalyst is loaded into the bed using an inert gas for the catalyst, such as nitrogen or argon. Injection of the catalyst at a location above the distribution plate 22 is an important feature. Since commonly used catalysts are very active, injection into the area below the distributor plate will initiate polymerization there, ultimately leading to plugging of the distributor plate. Instead, injection into the pot bed tends to help distribute the catalyst throughout the bed and eliminates the formation of high catalyst concentration local sites that could lead to the formation of "hot spots". Have.

Under a given set of operating conditions, the fluidized bed is maintained at a substantially constant height by withdrawing a portion of the bed as product at a rate equal to the rate of formation of the particulate polymer product.
Since the rate of heat release is directly related to product formation, the measurement of gas temperature rise (difference between inlet gas temperature and outlet gas temperature) to the reactor is determined relative to the rate of particulate polymer formation at a constant gas velocity. It becomes a factor.

The particulate polymer product is preferably withdrawn from the distribution plate 22 at or near point 34. Conveniently and preferably, the granular polymer product comprises a pair of timing valves forming a segregation zone 40.
It is withdrawn through the sequential operation of 36 and 38. While valve 38 is closed, valve 36 is opened to release the plug flow of gas and product into zone 40 between this zone and valve 36 and then valve 36.
To close. The valve 38 is then opened to feed the product to the external collection zone, and after feeding the valve 38 is closed to await the next product collection operation.

Finally, the fluidized bed reactor is equipped with a sufficient exhaust system to exhaust the bed during start and stop. The reactor does not require the use of stirring means and / or wall scraping means.

The reaction vessel is generally made of carbon steel and designed for the above operating conditions.

Polymers which are primarily relevant to the present invention and which give rise to the above-mentioned sheeting problems in the presence of titanium or vanadium catalysts are linear homopolymers of ethylene or high molar percentages (90%).
%) Ethylene and a small mole% (10%) of one or more C _{3 to} C ₈ α-olefins in a linear copolymer. C ₃ -C ₈ alpha-olefins should not also have a branched chain in any closer carbon atoms than the fourth carbon atom. Suitable
C ₃ -C ₈ alpha-olefins are propylene, butene-1, hexene-1 and octene-1. This description is not intended to exclude the use of the present invention for α-olefin homopolymer and copolymer resins where ethylene is not a monomer.

Homopolymers and copolymers have densities in the range of about 0.97 to 0.91. The density of copolymer, at a given melt index level is primarily regulated by the amount of C ₃ -C ₈ comonomer to be copolymerized with ethylene. That is, when the addition amount of the copolymer is gradually increased with respect to the copolymer, the density of the copolymer is gradually reduced. Various C _{3 to} C ₈ required to achieve the same result
The amount of comonomer varies from monomer to monomer under the same reaction conditions. Ethylene homopolymerizes in the absence of comonomers.

The melt index of a homopolymer or copolymer reflects its molecular weight. Polymers with a relatively high molecular weight have a relatively high viscosity and a low melt index.

[Examples] Having described the general nature of the present invention, specific examples of the present invention will be further described by the following examples. However, it will be understood that the invention is not limited to these examples only and that various modifications can be made.

Examples 1 and 2 described below are examples of conventional operations, and are carried out in the fluidized bed reactor shown in the accompanying drawings except that gas supply is a conventional method.
That is, the gas feed was introduced into the system via a route which feeds to the bottom of the reactor after the heat exchanger.

Example 1 (Comparative Example) Density of 0.918 g / cc, Melt Index of 1.0 dg / mm and 140
The fluidized bed reactor was started at operating conditions designed to produce a thin film grade low density ethylene copolymer product having a sticking temperature of ° C. The reaction was initiated by feeding the catalyst to a reactor which was precharged with a bed of granular resin similar to the product to be produced. The catalyst was a mixture of 5.5 parts titanium tetrachloride, 8.5 parts magnesium chloride and 14 parts tetrahydrofuran, which was previously dehydrated at 800 ° C. and treated with 4 parts triethylamylnium before deposition.
It was deposited on 100 parts of Davison Grade 952 silica and after deposition activated with 35 parts of tri-n-hexylaluminum. Reactor and resin bed at 85 ° C before starting catalyst feed
At the operating temperature of 1, the nitrogen was circulated through the resin bed to purge impurities. The concentrations of ethylene, butene and hydrogen were set to 53%, 24% and 11%, respectively. The cocatalyst was fed at a rate of 0.3 parts of triethylene aluminum per part of catalyst.

The reactor startup was normal. After 29 hours of product formation and equal to 6.5 times the weight of the fluidized bed,
A temperature change of 1 to 2 ° C higher than the floor temperature is 1/2 that of a gas distribution plate
It was observed using a thermocouple mounted inside the reactor wall at a height higher by the reactor diameter. Conventional experience has shown that such temperature changes positively suggest that a sheet of resin is being formed in the fluidized bed. At the same time, floor voltage (measured using an electrostatic voltmeter connected to a 1/2 inch diameter spherical electrode 1 inch above the reactor wall at a height that is 1/2 reactor diameter higher than the gas distribution plate) ) Is about +1500
It increased from a measurement of ~ + 2000 volts to a measurement above +5000 volts and then dropped to +2000 volts over 3 minutes. The changes in temperature and voltage continued for about 12 hours, increasing in frequency and magnitude. Over this period, sheets of fused polyethylene resin began to appear in the resin product. The occurrence of sheeting became more severe, that is, the temperature change increased to about 20 ° C higher than the bed temperature, remained at high temperature for a long time, and the voltage change became more frequent. The reactor was shut down due to the occurrence of sheeting.

Example 2 (Comparative Example) The fluid bed reactor used in Example 1 was started and operated to be suitable for extrusion or rotomolding and a linear low having a density of 0.934, a melt index of 5 and a sticking temperature of 118 ° C. A density ethylene copolymer was produced. By feeding a catalyst similar to the catalyst in Example 1 but activated with 28 parts of tri-n-hexylaluminum to a reactor pre-loaded with a bed of granular resin similar to the product to be made. , The reaction was started. The reactor and the resin bed were brought to an operating temperature of 85 ° C. and the impurities were purged with nitrogen before the catalyst feed was started. Ethylene (52%), butene (14%) and hydrogen (21%) were introduced into the reactor. The cocatalyst triethylaluminum was fed at 0.3 parts per part of catalyst. The reactor was operated continuously for 48 hours, producing resin equal to 9 times the amount of resin contained in the bed during this period. This 48
After a smooth run of time, a sheet of fused resin began to emerge from the reactor along with the normal granular product. At this point, the voltage measured at a height 1/2 reactor diameter above the distributor plate averaged +2000 volts and ranged from 0 to +10,000 volts, while skin thermocouples at the same height were The change was 15 ° C higher than the temperature. Two hours after the first sheet was seen in the product from the reactor, it was necessary to stop the catalyst and co-catalyst feed to the reactor to reduce the resin production rate. This is because the sheet blocked the resin discharge system. After 1 hour, the supply of catalyst and cocatalyst was restarted. The sheet formation continued and after 2 hours, the supply of the catalyst and the cocatalyst was stopped again, and carbon monoxide was further injected to stop the reaction. The voltage at this point is 12,0
It was 00 volts and the temperature change by the thermocouple continued until the poison was injected. Operate the reactor for 53 hours in total,
And, by the time the reaction was stopped due to sheeting, 10.5 times the volume of the resin of the bed was produced.

Example 3 (Example) A continuous polymerization of ethylene was maintained in a fluidized bed reactor. By supplying the catalyst and the cocatalyst to the reactor, 0.918 g / cm ³
A thin film grade low density copolymer having a density of 2 and a melt index of 2.0 dg / min was produced. The catalyst is 5 parts TiCl.
100 parts of Davison grade composed of a mixture of 1/3 AlCl ₃ and 7 parts of MgCl ₂ and 17 parts of tetrahydrofuran, which was pre-dehydrated at 600 ° C. and treated with 5.5 parts of triethylaluminum before deposition. It was deposited on 955 silica and activated after deposition with 33 parts tri-n-hexylaluminum and 11 parts diethylaluminum chloride. The cocatalyst, triethylaluminum, was fed in at a rate sufficient to maintain a 40: 1 Al: Ti molar ratio. Fluidized bed is 85 ℃
Maintained at the temperature of. The concentrations of ethylene, butene and hydrogen in the reactor were 34 mol%, 11 mol% and 8 mol%, respectively. Copolymer resin was periodically withdrawn from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed, all other feeds were introduced into the gas circulation upstream of both the heat exchanger and the compressor.

Then, various amounts of steam or oxygen gas in nitrogen were continuously fed simultaneously for several hours. The supply position was downstream of the compressor and upstream of the heat exchanger. The introduction rate of water or oxygen is indicated on a ppmw basis with respect to the removal rate of the copolymer from the reactor. During their introduction, both the inlet temperature of the circulating gas measured below the fluidized bed and the static voltage in the bed were monitored. A 1 ° C rise in inlet temperature is about 20
% Of the production rate declined. From the inner wall to the fluidized bed 1
By monitoring the voltage with a hemispherical steel probe placed in inches and at a floor diameter three times larger than the distributor plate,
The static voltage was measured. The measured values of catalytic activity and electrostatic voltage are shown below: Reactor operation was maintained smoothly throughout these tests. This example shows that introduction of impurity levels up to 7.8 ppmw produced little or no static voltage when impurities were introduced into the circulation path upstream of the heat exchanger.

Example 4 (Example) Again, continuous polymerization of ethylene was maintained in the fluidized bed reactor. A high density copolymer having a resin density of 0.946 g / cm ³ and a flow index (190 ° C., 21.6 kg) of 9 dg / min was produced by feeding the catalyst, cocatalyst and promoter to the reactor. The catalyst consisted of a mixture of 55 parts of VCl ₃ , 1.5 parts of diethylaluminum chloride and 13 parts of tetrahydrofuran, which was deposited at 100 ° C. on 100 parts of Davison grade 953 silica which had been previously dehydrated. Triethylaluminum was fed in such a proportion to maintain a 40: 1 Al: V molar ratio. Trichlorofluoromethane was fed in between the compressor and the heat exchanger in a molar ratio to triethylaluminum of 0.75: 1. The temperature of the fluidized bed was maintained at 100 ° C. The temperatures of ethylene, hexene, and hydrogen in the reactor were 73 mol%, 1 mol%, and 1.6 mol%, respectively. The other fluidized bed operations were the same as in the previous example.

Then, one concentration of steam and two concentrations of oxygen were introduced into the reactor over several hours each. These impurities were mixed with nitrogen and introduced into the circulating gas at a point just downstream of the compressor and upstream of the heat exchanger. When each of these impurities is being supplied to the circulation path,
Catalytic activity and electrostatic voltage were monitored as described in the previous examples. The results were as follows: The reactor operation was kept good while feeding these impurities. The result is that impurities introduced upstream of the heat exchanger at levels up to 9 ppmw with little or no effect on the electrostatic voltage due to different catalyst system and different resin properties than in the previous example. Is shown.

Example 5 (Example) A continuous polymerization of ethylene was maintained in a fluidized bed reactor. By supplying the catalyst and co-catalyst to the reactor, 0.918 g / cm ³
A thin film grade low density copolymer having a density of 2 and a melt index of 2.0 dg / min was produced. The catalyst is 5 parts TiCl ₃
100 parts Davison grade composed of a mixture of 1/3 AlCl ₃ and 7 parts MgCl ₂ and 17 parts tetrahydrofuran, which had been previously dehydrated at 600 ° C. and treated with 5.5 parts triethylaluminum before deposition It was deposited on 955 silica and after deposition activated with 33 parts tri-n-hexylaluminum and 11 parts diethylaluminum chloride. The cocatalyst, triethylaluminum, was fed in at a rate sufficient to maintain a 30: 1 Al: Ti molar ratio. The fluidized bed was maintained at 88 ° C. The concentrations of ethylene, butene and hydrogen in the reactor were 37 mol%, 12 mol% and 9 mol%, respectively. Copolymer resin was periodically withdrawn from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed and all other feeds were introduced into the gas circulation upstream of both the heat exchanger and the compressor.

A stream of nitrogen saturated with steam was then fed to the reactor downstream of the compressor and upstream of the heat exchanger. The water addition rate is 20 pp per 1 part of ethylene added to the circulating flow.
The amount of water was m. This water supply was continuously performed for 2.5 hours, and no static voltage change occurred in the fluidized bed during this time. The static voltage was kept at 0 volts over the period of water addition. The static voltage was measured by monitoring the voltage with a hemispherical steel probe provided in the fluidized bed 1 inch from the inner wall and 3 times the bed diameter above the distributor plate. The saturated water stream feed position was then moved immediately downstream of the heat exchanger. The amount of water added to this position was 8 ppm of water per 1 part of the amount of ethylene added to the gas circulation. When water was introduced to this new location downstream of the heat exchanger, a negative static voltage of -250 volts was immediately generated. Within 10 minutes after adding water downstream of the heat exchanger, the temperature indicated by the thermocouple installed on the side wall of the polymerization reactor in the fluidized bed zone was up to 92 ° C, that is, 4 degrees below the bed temperature.
C increased to a high temperature. This measurement indicated sheet formation at this location on the wall within the fluidized bed.

Example 6 (Example) Copolymerization of ethylene and butene was maintained in a fluidized bed reactor. The resulting copolymer was a thin film grade resin with a density of 0.918 g / cm ³ and a metre index of 1 dg / min. The catalyst consisted of 5 parts TiCl ₃ .1 / 3AlCl ₃ and 7 parts MgCl ₂ and 17 parts tetrahydrofuran, which was deposited on 100 parts Davison grade 955 silica. Silica was previously dehydrated at 600 ° C. and treated with 5.7 parts triethylaluminum before deposition,
After further deposition it was activated with 32 parts of tri-n-hexylaluminum and 11 parts of diethylaluminium chloride.
The catalyst triel aluminum was fed in a sufficient proportion to maintain a 30: 1 Al: Ti molar ratio. The fluidized bed was maintained at a temperature of 88 ° C. The concentrations of ethylene, butene and hydrogen in the reactor were 46 mol%, 16 mol% and 14 mol%, respectively. The resin was periodically withdrawn from the reactor to maintain a constant fluidized bed height within the reactor. The catalyst was fed directly into the fluidized bed and all other feeds were introduced into the circulating gas stream downstream of both the compressor and the heat exchanger.

The static voltage was measured in the fluidized bed by monitoring the voltage with a hemispherical steel probe 1 inch from the inner wall and 1 times the bed diameter above the distributor plate.

Then water to ethylene feed to ethylene feed to 0.
Added in an amount of 6 ppm. This water addition produced an immediate static voltage response from 0 to -1600 volts in the fluidized bed.

Then, the water addition point was moved from the downstream side to the upstream side of the heat exchanger, and the negative electrostatic voltage disappeared to 0 volt almost immediately.

Then, the water addition point was stopped three more times between the inlet and outlet of the heat exchanger. In each case of supplying water to the outlet of the heat exchanger, a negative voltage was generated, which disappeared immediately when water was supplied to the inlet of the heat exchanger. 3 parts of the circulating flow to the heat exchanger inlet with an amount of 0.8 ppm water per part of ethylene feed
Water continuously fed over time did not create an electrostatic voltage in the reactor.

Example 7 (Example) Using the same reactor producing resin under the same conditions as in Example 6, the effect of the water feed point on the electrostatic voltage in another case was tested.

In this example, the water supplied to the circulation stream to the heat exchanger outlet in an amount of 0.3 ppm per part of ethylene feed was placed in the fluidized bed--
It produced a static voltage of 500 volts. When the feed point was switched to the heat exchanger inlet, a water feed rate of up to 1.4 ppm per part of ethylene feed did not produce static voltage in the fluidized bed.
A continuous water feed rate of 1.2 ppm per part ethylene feed for 4 hours did not produce an electrostatic voltage in the fluidized bed.

Example 8 (Reference Example) Using the same reactor that produced the copolymer resin under the same conditions as in Examples 6 and 7, the effect of methanol feed point on static voltage and sheeting in the fluidized bed was examined.

In this case, when nitrogen saturated with methanol at 20 ° C. was first supplied to the reactor circulation stream to the heat exchanger outlet at a ratio of 1.3 ppm methanol per part ethylene feed, the static voltage in the reactor immediately Raised to +4000 volts. at the same time,
The thermocouple measured temperature on the inner wall of the reactor at a height of one plate diameter above the distributor plate increased from 86 ° C to 94 ° C, suggesting that a sheet had formed at this point.
At this point the reactor temperature was 88 ° C, so thermocouple measurements on all walls above 88 ° C suggest sheet formation.

When the methanol supply was switched upstream of the heat exchanger, the static voltage disappeared almost immediately to 0 volts. Furthermore, when methanol was supplied upstream of the heat exchanger, the thermocouple change of the wall portion which exceeded the temperature in the fluidized bed did not occur.

The methanol feed was clamped between the outlet and inlet of the heat exchanger a total of three times. In each case, a positive static voltage in the range of +700 V to +4000 V immediately occurs when methanol is supplied downstream of the heat exchanger, and this static voltage is 0 V when methanol is supplied upstream of the heat exchanger. Disappeared.

[Brief description of drawings]

The drawing is a schematic flow chart showing a typical gas phase fluidized bed polymerization process with some modifications to produce high density and low density polyolefins to illustrate the process according to the invention for reducing or eliminating sheeting. 10 …… Reactor, 12 …… Reaction zone 14 …… Velocity reduction zone, 16 …… Storage 18 …… Gas analyzer

Claims (7)

[Claims] 1. A gas provided with a circulation path for circulating a circulation flow composed of unreacted gas and solid particles, and cooling means and compressor means arranged in the circulation path for cooling and compressing the circulation flow. When polymerizing α-olefins with titanium-based catalysts or other catalysts, which tend to cause sheeting when sheet-forming amounts of water or oxygen are present as impurities, in phase-flow reactors, monomers and comonomers are used. Before cooling the circulation flow in the cooling means, the gas supply flow comprising an inert gas and hydrogen, the gas supply flow containing a sheet-forming amount of oxygen or water as an impurity of the gas supply flow. At the point of, and then cooling the circulating stream and the gas feed stream to direct them to the reactor. How to reduce the ringing. 2. A gas feed stream is introduced into the circulation stream at a point between the compressor and cooling of the circulation stream.
The method described. 3. The method according to claim 1, wherein one of the α-olefins is ethylene. 4. The method according to claim 1, wherein the inert gas is nitrogen. 5. The method of claim 1 wherein the other catalyst having a tendency to cause sheeting is a vanadium-based catalyst. 6. An alpha-olefin comprising a large molar percentage (90%) of ethylene and a small molar percentage (10%) of one or more.
The process according to claim 1, wherein a polymer consisting of a linear copolymer with a C ₃ -C ₈ α-olefin is polymerized. 7. The method according to claim 6, wherein the polymer is a homopolymer or copolymer of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, heptene-1 or octene-1.